In recent years, the following voice synthesis techniques have been proposed. Examples of such proposed voice synthesis techniques include a technique that synthesizes and outputs voice corresponding to a speaking tone and voice quality of a user and thereby generates voice in a more human-like manner (see, for example, Patent Literature 1), and a technique that analyzes voice of a user to diagnose psychological and health states etc. of the user (see, for example, Patent Literature 2).
Also proposed in recent years is a voice interaction or dialogue system which implements voice interaction with a user by outputting, in synthesized voice, content designated by a scenario while recognizing voice input by the user (see, for example, Patent Literature 3).